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                         At this time of year when it is getting colder this is probably battery related. If you have a dodgy battery they usually give up the ghost on the first frost! 
Try using jump lead from another car - if it starts then probably the battery . Before you replace it test the voltage of the battery with the engine running. If not well over 12v (usually 13+)  then the alternator may be suspect instead. 
                            
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